An Operator-Splitting Scheme for Viscosity Solutions of Constrained Second-Order PDEs

This work presents a novel operator-splitting scheme for approximating viscosity solutions of constrained second-order partial differential equations (PDEs) with low-regularity solutions in \( C(\overline{\Omega}_T) \cap H^1(\Omega_T) \). By decoupling PDE evolution and constraint enforcement, the scheme leverages stabilized finite elements and implicit Euler time-stepping to ensure consistency, stability, and monotonicity, guaranteeing convergence to the unique viscosity solution via the Barles-Souganidis framework. The method supports vector-valued constraints and unstructured meshes, addressing challenges in traditional approaches such as restrictive stability conditions and ill-conditioned systems. Theoretical analysis demonstrates a convergence rate of \( O(h^{1-\epsilon}) \) with a proper chosen time step. Applications to Hamilton-Jacobi equations, reaction-diffusion systems, and two-phase Navier-Stokes flows highlight the scheme's versatility and robustness, positioning it as a significant advancement in numerical methods for constrained nonlinear PDEs.